Magnetic multilayer films are employed as a storage element in memories, such as magnetic random access memories (MRAM) and the like. The memory element for the MRAM technology is a patterned structure (memory bit) of multilayer material. The magnetic multilayer material is usually composed of a stack of different materials, such as permalloy (NiFe), cobalt-iron, copper, tantalum, etc. and may include some insulator like materials, such as Al2O3. A typical stack may contain as many as ten different or more overlying layers of these materials. To fabricate a storage element, it is necessary to deposit the materials in overlying blanket films, layer by layer, to form a patterned layer of photoresist (resist), and to etch the films into appropriate structures.
Ion beam milling or ion beam etching processes have been employed to remove magnetoresistive materials. Ion beam milling is a physical milling process. Areas that are not protected by the mask are removed by bombardment with ions. The bombardment of ions sputters or peels away the unprotected material. Ion beam milling operates with relatively low selectivity, and the portions of the stack that are near to the edges of the mask or the boundaries of an MRAM cell body can be easily damaged.
Chemical etching techniques have also been employed to selectively remove portions of deposited sheets. Examples of chemical etching techniques include dry etching techniques and wet etching techniques. After completion of the reactive etch of the multilayer material, the remaining portions of the stack are typically exposed to a post-etch passivation plasma.
One of the drawbacks of current etching techniques is that the vertical profiles of MRAM structure are susceptible to electrical shorting across the thin tunnel junction. As illustrated in FIG. 12 the MRAM structure 300 has straight vertical walls (vertical relative to the plane of the surface being etched). The vertical walls adjacent the thin alumina insulator layer separating the upper magnet and the lower magnetic is inadequate to prevent electrical shorting.